Measurements of External Radiation in United States Dwellings

Abstract

The results of a survey of terrestrial gamma radiation levels are reported for the United States. This database represents a total of 1074 measurements nandaround 247 different dwellings in several different areas of the country. The absorbed dose rate in air outdoors was found to range between 14 and 118 nGy.h-1 and averaged 46.6 nGy.h-1, while for indoors it ranged between 12 and 160 nGy.h-1 and averaged 37.6 nGy.h-1. Apart from regional differences in the terrestrial gamma levels, variations of up to a factor of 2 can be seen in the same geographical area. Variations within a house are typically large, with basement living areas averaging 50% higher than second-floor areas. Houses of full brick construction had average indoor levels 50% higher than those for wood frame houses. The material used for interior wall construction was not found to strongly influence the indoor dose rates except for rooms containing brick, cinder block or stone. For wood frame houses, including those of brick veneerexteriors, alinear regression analysis indicates that the average indoor dose rate can be reasonably well predicted based on a constant, which related to the building contribution, and a shielding factor for the outdoor dose rate. Using the data collected in this survey and the population weighted mean outdoor absorbed dose rate in air reported for the US, the corresponding mean indoor value is estimated to be 37 nGy.h-1. This value is in the low end of the range reported for other countries and is about half the estimated worldwide average of 70 nGy.h-1.